The present invention relates to rotary fluid pressure devices such as low-speed, high-torque gerotor motors, and more particularly, to a novel valve drive arrangement for such motors.
Low-speed, high-torque gerotor motors of the type to which the present invention relates are typically classified, in regard to their method of valving, as being either "spool valve" motors, or "disc valve" motors. As used herein, the term "spool valve" refers to a generally cylindrical valve member in which the valving action occurs between the cylindrical outer surface of the spool valve, and the adjacent, internal cylindrical surface of the surrounding housing. The term "disc valve" refers to a valve member which is generally disc-shaped, and the valving action occurs between a transverse surface (perpendicular to the axis of rotation) of the disc valve and an adjacent transverse surface.
Although the present invention may be utilized with either a spool valve or a disc valve gerotor motor, it is especially advantageous when used with a spool valve motor, and will be described in connection therewith.
Spool valve designs are especially well suited for use with relatively smaller gerotor motors, especially where it is desired to minimize the transverse cross-sectional configuration of the motor. The configuration of the spool valve motor which is the most common, commercially, is one in which the spool valve is formed integral with the output shaft and therefore, is located "forwardly" of the gerotor. One disadvantage of this particular configuration is that the spool valve necessarily has a fairly thin wall, and pressures in the range of 2,000 PSI can cause sufficient radial shrinkage of the spool valve to diminish the volumetric efficiency of the motor.
Another configuration which is known is to locate the spool valve "rearwardly" of the gerotor, but substantially increase the wall thickness of the spool to avoid the radial shrinkage problem and the resulting reduction in volumetric efficiency. However, in such a configuration, the methods for transmitting orbital and rotational movement of the gerotor star into rotational movement of the spool valve which are known in the prior art, result in either substantial complication of the motor design, or an increase in the axial length of the motor.